Sex change

The early persons of chandravamsa and suryavamsa are as

An interesting point in the development of these two families is that Same Person Was

1. Sudyumna the fifth descendent on the Suryavamsa side used to be male for one month and 
2. on the Chandravamsa side female for one month. He used to be called Sudyumna and Ila respectively during these months.

http://en.wikipedia.org/wiki/Ila_(Hinduism)